This invention relates to drop tubes and more specifically to a new fill liquid restriction apparatus for such drop tubes.
Riser pipes are used as the main liquid fill lines for fuel storage tanks located below ground at gasoline service stations and the like. The riser pipe is vertically oriented, has its upper end located in a manhole, and its lower end opening towards the inside of the below-ground storage tank. Because it is important to fill fuel storage tanks from the bottom of the storage chamber, drop tubes are inserted through the riser and have their outlet ends positioned near the bottom of the storage chambers. Risers and drop tubes must be dimensioned to accommodate a flow of 340 gallons per minute.
Another function attempted to be performed by drop tubes includes cutting of the delivery flow when the storage tank is nearly full and bleeding into the tank the fuel remaining in the riser and delivery hose after the delivery truck operator closes the valves on the truck. Apparatus purporting to perform these functions include drop tubes fitted with a valve section located near the top of the storage chamber. A float member located outside the drop tube rises as the liquid level approaches the top of the chamber. When the float reaches a predetermined upward position, the float causes a shut-off valve to enter the path of the delivery fuel stream. The force of the stream closes the shut-off valve against a valve seat thus sealing closed the main delivery opening in the drop tube. Additional valves and ports may be provided to bleed the fuel remaining in or thereafter entering the riser pipe either into the storage tank chamber or through a by-pass channel to the lower part of the drop tube.
Many problems arise from the presence of these shut-off valve sections in drop tubes. For example, the valves and their many associated moving springs, cams and pins break or become defective due to the repeated slamming of the valve. Also, operators repeatedly drop their long gauge sticks down through the riser/drop tube and damage the valve seats and perhaps the stick itself.
These problems could lead to the valve remaining in its closed position even when the float falls to its lowest position. In this case the drop tube must be pulled from the tank for repair.